The present invention relates to elevators. It applies, in particular, to elevators having a shallow pit and/or a low overhead.
Elevators with a shallow pit and/or a low overhead are advantageous because of the reduced impact of their installation on the construction cost and because of their compatibility with severe architectural constraints.
Machine room-less elevators have their drive system, in particular their motor and brake, located inside the volume of the elevator shaft. Access to these parts, and to other components fitted in the shaft is required for maintenance or repair purposes. Standards such as EN81 require safety clearances at the top and at the bottom of the shaft so that a person can enter a safe working space to have access to the machines and shaft components. Such working space can be located in the upper part of the hoistway, with the operator standing on top of the car, or in the pit at the bottom of the shaft.
Safety measures to make sure that the minimum safety volume is always achieved in an inspection operation have been proposed, in particular by taking advantage of the safety brake usually present in the elevator structure to prevent the car from traveling at an excessive speed. The safety brake is typically mounted on the car and cooperates with the fixed vertical guide rails to frictionally stop the car when triggered by a speed limiter cable or rope. US 2004/0222046 and WO 2006/035264 disclose devices for securing the protective space at the top or bottom of the shaft, including a fork element receiving the speed limiter cable. A bulging part is fixed on the cable to form an abutment caught by the fork element at a vertical position corresponding to the desired protective space, which triggers the safety brake. In a normal operation of the elevator, the fork element is retracted out of engagement with the limiter cable and the bulging part, so that the car can reach the uppermost or lowermost landing level unhindered. A spring mounting is provided for the fork element, so that when it catches the bulging part, it is allowed to move vertically for a certain distance needed for the safety brake to stop the car. The stroke of the spring mounting corresponding to such distance depends on the inertia of the car and counterweight and should typically be about 100 to 200 millimeters.
A problem with this kind of safety device is that the fork element may, for various reasons, become jammed and unexpectedly remain in the retracted position when an inspection operation is started. This creates a danger for the personnel entering the hoistway.